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as your speed, your baseline exposure speed is 1/500ths (or 1/2000ths at
400ISO). Using a 2x converter will cost you two stops and so you drop to an
almost unmanageable 1/125th if you stay on ISO 100. Using a converter is a
double whammy, you need faster shutter speeds to accommodate the higher
magnification, but you are losing aperture at the same time. As with all
photography, the settings are a compromise between camera shake, subject speed,
digital noise and sometimes the simple need to just get a shot at all costs!

Shutter Speed Selection

Assuming that you need sharp images, it is possible to compute the required
shutter speed to stop action under various circumstances. Typical subject speeds
are shown in the table (they vary – international class athletes go faster, hit
faster, bowl faster, etc). For a 300mm lens the shutter speeds at various
distances and speeds are shown. By way of example if we take a hockey player
moving at 20mph (equivalent to12s for 100 metres) and a distance of 20m, we
require 1/6000th to stop the action. This would need an aperture of f2.8 and an
ISO of 200 in bright sunshine, close to the limit of available technology.
If the subject is now a bowler, he will be at 60m minimum but you have to add
the arm action to his basic speed of 20mph, which brings the ball speed up to
close to 90mph for a test bowler. Again this demands a shutter speed of
1/4000th. With an 800mm lens you would have to go to 400ISO, probably faster.

These calculations assume that stopping action is vital. In reality this is not
so. Aesthetics demands a bit of blur to create a sense of movement. The trick is
to make it look like you meant it, not that you were incompetent! Note two other
things. An image stabilising lens is of no help in stopping subject movement,
all it will do is prevent you from adding camera shake to an already slightly
fuzzy subject. The calculations assume that the subject is moving across the
field of view. If the action is coming diagonally towards you, you can grab
about a half stop to your benefit; if the action is directly towards you, you
can grab just over a stop.

This assumes that the subject is moving at a single speed. However, a bowler
running up to deliver is going at 20mph and if you are panning at that speed he
is stationary on the film. However his arm is moving at 70mph at the ball but is
effectively at zero mph at the shoulder. The ground is moving at an effective
-20mph (backwards across the frame) which is why it is possible to have a near
sharp bowler and a nice blur on the crowd in the background.

The speed differential is even greater if you are panning a racing car. Here the
axle of the wheel has zero translational speed, the bottom of the wheel is
stationary (if you are panning exactly) but the top of the wheel is moving
forward at twice the speed of the vehicle. While all this is going on the
rotational speed of the wheel is whatever it is. The net effect is almost sharp
writing on Jensen Button’s helmet, a blurred background and rotationally blurred
wheels. If, in addition, the car is pitching under braking or due to a bumpy
surface then only the logos in the centre of that pitching motion will be sharp.
This is an effect you can sometimes see on motorbikes as they dig their noses in
under heavy braking into a bend.